The problem can be corrected by upgrading the affected package to
version 7.4.5-3ubuntu0.4. In general, a standard system upgrade is
sufficient to effect the necessary changes.

Details follow:

The execution of custom PostgreSQL functions can be restricted with
the EXECUTE privilege. However, previous versions did not check this
privilege when executing a function which was part of an aggregate.
As a result, any database user could circumvent the EXECUTE restriction of
functions with a particular (but very common) parameter structure by
creating an aggregate wrapper around the function. (CAN-2005-0244)

Several buffer overflows have been discovered in the SQL parser. These
could be exploited by any database user to crash the PostgreSQL server
or execute arbitrary code with the privileges of the server.
(CAN-2005-0245, CAN-2005-0247)

Finally, this update fixes a Denial of Service vulnerability of the
contributed "intagg" module. By constructing specially crafted arrays,
a database user was able to corrupt and crash the PostgreSQL server.
(CAN-2005-0246). Please note that this module is part of the
"postgresql-contrib" package, which is not officially supported by
Ubuntu.